Pumping system for low-density gas flow in space chambers and wind tunnels

ABSTRACT

A low-density cryopumping system for pumping high velocity high temperature, directed gas flow from a wind tunnel and/or rocket nozzle by means of condensation on a structure consisting of a series of condensing surfaces positioned downstream of the nozzle, and oriented in spaced-apart relation to each other and parallel to the gas flow to thereby permit the flow to initially bypass therethrough for direct impingement against a precooling structure positioned further downstream from the condensation structure. The gas is thereby cooled and thereafter deflected upstream in diffused manner for its subsequent impingement against, and condensation and collection on, the condensing surfaces.

United States Patent Stephenson [54] PUMPING SYSTEM FOR LOW-DENSITY GASFLOW IN SPACE CHAMBERS AND WIND TUNNELS [72] Inventor: William B.Stephenson, Tullahoma, Tenn.

[73] Assignee: The United States of America as represented by theSecretary of the Air Force (22] Filed: Aug. 19, 1970 [21] Appl.No.:65,048

3,149,775 9/1964 Pagan0.... ..62/55.5 3,286,531 11/1966 Shapiro..62/55.5

Primary Examiner-William J. Wye Attorney-Harry A. Herbert, Jr. andArthur R. Parker [5 7] ABSTRACT A low-density cryopumping system forpumping high velocity high temperature, directed gas flow from a windtunnel and/0r rocket nozzle by means of condensation on a structure consisting of a series of condensing surfaces positioned downstream of thenozzle, and oriented in spaced-apart relation to each other and parallelto the gas flow to thereby permit the flow to initially bypasstherethrough for direct impingement against a precooling structurepositioned further downstream from the condensation structure. The gasis thereby cooled and thereafter deflected upstream in diffused mannerfor its subsequent impingement against, and condensation and collectionon, the condensing surfaces.

10 Claims, 4 Drawing Figures PUMPING SYSTEM FOR LOW-DENSITY GAS FLOW INSPACE CHAMBERS AND WIND TUNNELS BACKGROUND OF THE INVENTION Thisinvention relates generally to the field of cryopumps and, inparticular, to their use in pumping high-velocity directed gas flows bymeans of condensation.

Although cryopumping systems have been extensively utilized in theremoval of static gases from vacuum systems, their use in the pumping ofhighvelocity directed flows has, however, been somewhat limited sincethe direct application thereto of the static pumping data forcondensation has not been immediately obvious. In this regard, bothmolecular beam and supersonic low-density wind tunnel experiments haveshown that, for relatively low-energy fluxes, practically all of theincident flux or flow is condensed on a surface normal to the stream,provided the surface temperature remains low enough. However, when thetotal enthalpy of the stream is high, as for rocket exhausts, it may beimpossible to maintain the pumping surface temperature low enough,unless, as taught by the present invention, some kind of two-step systemis utilized in which a precooling stage is used to initially extract thebulk of the sensible heat before the gas reaches the pumping(condensing) surface. In this connection, it has been determined thatthe precooling stage should be placed downstream of the condensingstage, since its positioning upstream thereof may result in largepumping losses.

Where a hot multispecies directed gas stream is present, the pumpingsystem should comprise successively colder stages which (I) remove heatand (2) condense or absorb the various components thereof in a series ofsteps. In the case of rocket exhaust streams, the components thereof areusually condensable on liquid nitrogen cooled surfaces at a temperatureof 80 K., conventional gaseous helium cooled surfaces at 20 K., andfurther absorbable on lower temperature surfaces at 420 K.

Previous attempts to maintain a low pressure in a space environmentwhere a high-temperature jet introduces gas into a chamber have involved(1) allowing the chamber pressure to rise by several orders, whichobviously is a disadvantage, (2) the provision of a very large capacityrefrigeration system for the removal of both the sensible heat and thecondensation heat of the jet and (3) the introduction of a precoolingarray of surfaces ahead of the condensing surface to extract the bulk ofthe sensible heat. Both the methods of (1) and (3) above have provenunsatisfactory, the method of (I) obviously allowing an unfavorableincrease in chamber pressure, and the precoolers involved in the methodof (3) above, that have been designed to date, having transmitted nomore than fifty (50) percent of the flow, the remainder being returned,again, to unfavorably increase the chamber pressure. Solution (2) abovehas proven not feasible because of the high cost of refrigerationcapacity at low temperatures. The present invention avoids theaforementioned unsatisfactory aspects by utilizing the directionalcharacter of the jet flow to minimize heat transfer to the condensingsurfaces. The stream is cooled and rendered diffuse so that it isreadily pumped by the relatively long passages inherently formed by andbetween the condensing surfaces, as will be further describedhereinafter. In particular, the concept of the present inventionmaintains a low-environmental chamber pressure and, furthermore,minimizes the low-temperature refrigeration requirements by a unique andyet simplified arrangement to be hereinafter disclosed in the followingsummary and detailed description thereof.

SUMMARY OF THE INVENTION The present invention consists briefly in acryopumping system for a wind tunnel or rocket which has as itsprincipal object the pumping of a high-velocity, directed gas flow bythe use of condensing surfaces incorporated downstream of the tunnel orrocket nozzle. The temperature of the flow is initially lowered by aprecooling system located further downstream from the condensingsurfaces. The latter are spaced apart and oriented parallel to thestream to thereby permit the flow to initially bypass therethrough forits direct impingement against, and precooling by, the precoolingsystem, which includes separate precooling portions for both the axialand radial flow components. The precooled gas is thereby deflected, indiffused manner, back upstream for substantial impingement against, andcondensation and collection on the condensing surfaces. A separate setof condensing surface are used for condensing both the precooled radialand axial components of the gas flow.

Other objects, as well as advantages, of the invention will becomereadily apparent from the following disclosure thereof, taken inconnection with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents a schematicillustration of the elementary two-stage cryopumping system conceptutilized in the present invention, as it may be applied to one series ofcondensing surfaces;

FIG. 2 is another schematic view, showing the basic configurationincorporating the concept of the present invention, as it may be appliedto the hot multispecies, directed gas stream of a rocket, for example;

FIG. 3 is a perspective view, partly schematic and brokenaway,illustrating details of the preferred form of the inventive cryopump;and

FIG. 4 is an additional partially schematic and broken-away view,showing further details of the cooling system utilized for both theprecooling and condensing stages of the inventive arrangement of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring generally to thedrawings, and, in particular, to FIG. 1 thereof, the basic or elementarytwo-stage system involved in the present invention is indicatedgenerally at 10 as including a cooling surface at 11 and a condensingsurface at 12, the latter being formed into a tubelike configuration.The two-stage system was developed, in accordance with the teaching ofthe present invention, when it became evident that, although relativelylow-energy fluxes may be satisfactorily pumped by condensation alone,for relatively highenergy fluxes, a large fraction of the heat must beextracted, before the gas reaches the condensing surface, by means of aprecooling surface. It has been determined that, if the said precoolingsurface is placed upstream of the condensing surface, the directedcharacter of the flow is destroyed, and at least half of the scatteredgas is reflected upstream. To obviate this difficulty, the precoolingsurface, as at Ill, for the present invention, may be located downstreamof the condensing surface, as at 12, and thereby effectively blocks orcloses the downstream end thereof. Moreover, since the axis of the tubeconfiguration formed by the said condensing surface 11 is orientedparallel to the flow vector, the incident flux or flow, indicatedgenerally at 13, is permitted to bypass therethrough and impingedirectly against the cooling surface 11, where it is precooled.Thereafter the uniform incident flow impinging against the surface 11 isconverted into random flux and diffuses upstream from section A" (NoteFIG. 1), as is schematically indicated at the reference numeral 14. Partof this flux is thereby transmitted and then intercepted and condensedon the walls of the tube or condensing surface 12, and a part thereof,corresponding to the efflux at outlet or upstream end at the sectionmarked Bf represents the fraction thereof not condensed and thereforenot captured by the pump 10. Very little of the incoming flow from theincident flux I3 is intercepted by the condensing surface 12 due to thelatters previously noted parallel orientation. However, because of itsunique orientation, the latter surface I2 offers a large interceptionarea to the diffusely returning flux, after the latter has initiallyimpinged against, and been precooled by the configuration is to ahigh-enthalpy stream composed of 5 several species that are mostefficiently condensed or absorbed on different surfaces. The cryogeniesavailable may be used to supply cooling to surfaces at about 80 I(.,l2-25 K., and 2-5 I(., respectively, for liquid nitrogen, gaseoushelium, and liquid helium. In addition to direct condensation, cryogenicadsorption appears to be feasible for pumping hydrogen. In FIG. 2, forexample, there is illustrated a schematic array of cooling andcondensing surfaces, indicated generally at 15, that is designed to pumpa hot gas stream comprising species which may, for example, condense atthe aforementioned temperatures of 80 K., 20 K., and 4.5 I(.,respectively. Thus, if these three cryogenic media are made available atthe respectively lower temperatures, T,, T T as indicated above, thethree-stage pumping arrangement of FIG. 2 is made effective for pumpinga stream comprising components N., N and N; which may comprise theaforesaid coolants and which respectively condense at the threesuccessively lower temperatures of T,,=80 K., T =2O K., and T =4.5 K.Thus, with the arrangement of FIG. 2, all the incident flow at 16comprises components N N and N passes through the array until it isarrested and cooled at the 80 K. temperature section (T indicated at 17,which is at the extreme downstream end of the array. At this surface 17,the first condensable component, N is condensed and pumped. Theremaining species, N and N diffuse upstream into the 20 K. temperature(T array at station A, as depicted at 18, where the major part of thesecond species N is condensed and pumped. However, a fraction, F of the20 K. condensable species, N is transmitted through section B, asindicated at 19, as well as all of the third species N;,, as indicatedat 20. The 4.5 temperature condensing surface transmits and condenses afraction, F of the third species, N plus most of the 20 K., secondspecies N leaving a portion or fraction F of the second species N and afraction of F N to be rejected at the section C" and therefore notpumped, as indicated generally at 21.

The arrangement of the condensing surfaces through which the directedstream passes may be in the form of rectangular or hexagonal cells,concentric cones, or parallel plates, like a venetian blind. Thespecific embodiment of the invention to be hereinafter disclosed inconnection with FIGS. 3 and 4 is an example of one such configurationwhich is currently utilized in a test facility. As viewed particularlyin the aforesaid FIG. 3, the unique pumping system of the presentinvention is indicated generally at 22 as being enclosed within an outerwall surface 23, which may represent the chamber wall of a lowdensity-research wind tunnel and/or space propulsion test facility.Pumping system 22 may comprise a first, pair of cooling surfaces 24 andrespectively, for cooling the radial and axial components of the gasflow. Surfaces 24 and 25 may be maintained, for example, at thepreviously mentioned temperature of 80 K. or T Said pumping system 22may further comprise a second, pair of condensing plate surfacestructures at 26 and 27, respectively, which correspond to theappropriately positioned cooling surface 24 and 25. On the one hand,cooling surface 24 is concentrically arranged within the outer researchchamber wall 23 and is further positioned in surrounding relation to thecondensing plate surface structure 26. Moreover, cooling surface 24 isfurther oriented normal to, and is utilized to intercept and initiallycool the radial component of a high-velocity gas flow, indicatedgenerally and schematically at 28, which is being emitted or exhaustedfrom a nozzle at 29, the latter constituting either the wind tunnel orrocket nozzle. On the other hand, the cooling surface 25, which ismounted in blocking position downstream of the downstream ends of thecondensing surface structure 27, is likewise further oriented normal to,and thereby intercepts and initiallycools the axial component of theaforesaid gas flow 28. After its initial precooling by the said coolingsurfaces 24 and 25, the gas flow is then returned upstream in greatlydiffused form.

Condensing plate surface structure 26 may consist of a plurality ofhorizontally and circumferentially disposed relatively elongated plateelements arranged in spaced apart and parallel relation to each other.Moreover, they may be concentrically arranged relative to, and withinand in slightly spaced relation to the said cooling surface 24, asclearly depicted in the aforesaid FIG. 3. Condensing plate surfacestructure 27 likewise may consist of a plurality of vertically disposed,spaced apart and parallel plate elements positioned in front andupstream of the cooling surface 25. An important feature of bothcondensing surface structure-plate elements 26 and 27 resides in theirparallel orientation relative to the gas flow 28 which ensures theinitial bypass of the flow through the latter structure for its initialdirect impingement on, and precooling by the cooling surfaces 24 and 25.In this manner, the present invention uniquely provides for theextraction of considerable heat from the gas flow prior to the latterscondensation on the condensing surface structures 26 and 27. Moreover,the relatively elongated configuration of said condensing surfacestructures 26 and 27 provides what is, in effect, a series of long ductsensuring a greater interception area and therefore much improvedcondensation to the gas flow, after the latter has been precooled andthereafter diffusely returned upstream.

The gas flow 28 to be cooled and condensed, which corresponds to thepreviously described incident flow of FIG. 2, may be composed of asingle species N,, as in the case of the wind tunnel, or multiplespecies N,+N N,,, as in the case of a rocket exhaust plume. A suitablefirst, low temperature coolant at the previously described temperature Tand consisting, for example, either of gaseous helium at 20 K., orliquid hydrogen, may be supplied to the condensing surface structures 26and 27 from a first refrigeration system (not shown), through a supplyor inlet line at 30 in the direction indicated by the arrow A, by way ofa first, intake manifold at 31. Said low-temperature coolant may bethereafter collected by a second manifold at 32 for its subsequentreturn to the said first refrigeration system by way of the return lineat 33, the direction of said coolant flow being indicated at the arrow Asuitable second coolant at the previously suggested higher temperature,T K., may be similarly supplied to the cooling surfaces 24, 25 from asecond refrigeration system (not shown) by means of the supply line at34 in the direction indicated at the arrow C, through third and fourthmanifolds, indicated at 35 and 36, respectively, and thereaftercollected by a fifth and a sixth manifold, indicated at 37 and 38,respectively, for return to the said second refrigeration system bymeans of the return line at 39 in the direction of flow indicated at thearrow D."

With particular reference to FIG. 4, which illustrates only the coolingsurface 24 and the condensing surface structure 26 for the sake ofclarity, it is clearly illustrated that the previously describedrelatively high temperature T. 80 K., for example, coolant istransferred between the manifolds 35 and 37 by means of coolantchannels, indicated at 40, which may be integrally formed to the outercircumference of the said cooling surface 24 and interconnectedtherebetween. For the transfer of the previously noted, low temperature,T 20 I(., coolant between the aforementioned manifolds 31 and 32, thecoolant channels indicated at 41 as being integrally or otherwise formedwithin the individual elements comprising the condensing surfacestructure 26 may be utilized for interconnection between said last-namedmanifolds. Similarly designed interconnecting coolant channels (notshown) may also be utilized for transferring coolant between themanifolds 36 and 38, respectively, used for the cooling surface 25 andcondensing surface structure 27 (Note FIG. 3).

In operation, as seen in both FIGS. 3 and/or 4, both radial and axialcomponents of the high-velocity gas flow 28 from the nozzle 29 passesbetween the condensing surfaces 26 and 27 and impinges directly oncooling surfaces 24 and/or 25 (cooling surface 24 and condensing surfacestructure 26 only are shown in FIG. 4), due to the parallel andspaced-apart orientation of the said condensing surface structures 26and 27 to the direction of flow, where, according to classical slipflow, or molecular flow theory with an accommodation of unity, themolecules leaving the cooling surfaces 24 and 25 will be at atemperature in equilibrium with that of the surfaces 24, 25. To ensurethe diffuse flow of the intercepted gas flow from the surface of each ofthe cooling surfaces 24 and 25, the latter may be formed with a groovedsurface configuration, as indicated, for example, at 24a in FIG. 4 forthe surface 24.

As previously indicated with particular reference to FIG. 2, a largeportion of the diffuse flow leaving the cooling surfaces 24, 25 willimpinge on the condensing surface structures 26 and 27 where it will becondensed and captured, provided, of course, the condensing surfacetemperature is maintained at the condensing temperature in the mannerhereinbefore described for the unique arrangement of the presentinvention. Moreover, to facilitate both the transfer of the coolant flowbetween the manifolds, such as at 31 and 32, as well as to foster orimprove the condensing action of each of the said condensing surfacestructures 26 and 27, the latter may be each fabricated from a flatcentral plate element, as at 26a in FIG. 4, each of which plate elementmay be integrally formed with a coolant channel, such as was previouslydescribed at 41. Furthermore, the said central plate element may befurther formed with an outer surface portion that incorporates acontinuous configuration comprising a plurality of triangular, or othersuitably shaped outwardly projecting pointed elements, as at 42, whichcollectively form a series of condensation-collecting channelsinterspersed therebetween and thereby greatly improves the condensingand collecting of the said condensation surface structures 26 and 27Although the foregoing description of the operation of the inventivepumping system was based on an assumed accommodation coefiicient ofunity; in actual practice, this coefficient will not be unity, but mayapproach it and values of 0.8 to 0.9 have been quite common.Furthermore, when the flow is composed of rocket exhaust gases, or othermulticomponent gases, some components having higher condensationtemperatures and therefore more easily condensable, the cooling surfaces24 and 25 of the improved mechanism of the present invention willcondense such more easily condensed constituents, thus reducing the heatload that must be handled by the more expensive low-temperaturecondensing surfaces 26 and 27.

Thus, a new and improved high-velocity gas flow pumping system has beendeveloped wherein the low-temperature condensing surfaces 26 and 27thereof are not required to accept the heat load of gases that willcondense at higher temperatures; the gas flow is precooled beforestriking the said low temperature condensing surfaces, thereby evenfurther reducing the refrigeration requirements for the requiredcondensation; and the arrangement of the condensing surfaces 26 and 27in a series of long duct configurations insures that a large fraction ofthe steam is condensed.

We claim:

1. A cryopumping system for application in a low-density researchchamber-wind tunnel and/or space propulsion test facility having ahigh-speed nozzle for emitting a high-energy gas flow therefrom, andcomprising; condensing means located in the chamber downstream of thenozzle and incorporating open-ended passageways oriented in a first,predetermined manner relative to the chamber axis, and corresponding toa first position in direct communicating and parallel relation with, andthereby initially receiving and bypassing therethrough the expandingflow of the high-energy gas being emitted from said nozzle, without anysubstantial condensation resulting therefrom; cooling means positionedwithin the chamber at a position therein downstream of the condensingmeans and being further oriented in a second, predetermined mannercorresponding to a second position directly in the path of, and therebyensuring the initial interception and substantial precooling of the gasflow being initially bypassed through the said open-ended passageways ofsaid condensing means; said initially intercepted gas flow being therebyand thereafter returned upstream in a diffused condition, and thereforeat a substantial angle to its original flow, after its initial, directimpingement with said cooling means, for its subsequent and substantialinterception by, and condensation on, a substantial intercepting areaof, the open-ended passageways of said condensing means; and separatecoolant supply and return means adapted to respectively supply coolantat successively lower temperatures to said cooling and condensing means.

2. In a cryopumping system as in claim 1, wherein the openendedpassageways of said condensing means includes separate, first and secondcondensing-passageway portions perpendicularly-arranged relative to eachother and respectively oriented in parallel relation to both radial andaxial-flow components inherent in the expanding gas being emitted fromsaid nozzle.

3. In a cryopumping system as in claim 2, wherein said firstcondensing-passageway portion comprises a first, plurality ofhorizontally extending and circumfierentially-disposed, condensing plateelements arranged in spaced-apart relation to each other, and inparallel relation to the radial component of the said gas flow resultingfrom its radially outward expansion after leaving the chamber nozzle;said condensing plate elements thereby forming said firstcondensing-passageway portion into a plurality of gas flow-bypassingducts aligned in substantially parallel relation to, and thus ensuringthe bypass therethrough of the radial component of said gas flow.

4. In a cryopumping system as in claim 2, wherein said secondcondensing-passageway portion comprises a second, plurality ofvertically disposed, condensing plate elements oriented in both spacedapart and parallel relation to each other, and in parallel manner to theaxial component of the said gas flow.

5. In a cryopumping system as in claim 4, wherein said cooling meanscomprises a first, precooler device oriented outwardly of, and at afirst predetermined angular relation to said first, plurality ofhorizontally disposed, condensing plate elements to thereby ensure thedeflection of the radial component of said precooled initial gas flowagainst a relatively large interception area formed by said condensingmeans.

6. In a cryopumping system as in claim 5, wherein said cooling meansfurther comprises a second precooler device positioned downstream of,and oriented at a second predetermined angular relation relative to saidsecond, plurality of vertically disposed, condensing plate elements tothereby ensure the deflection of the precooled gas flow against themaximum area of interception of said last-named condensing plateelements.

7. In a cryopumping system as in claim 5, wherein said first precoolerdevice comprises a grooved and arcuate-shaped, cooling surfacecircurnferentially disposed in spaced relation to, and radiallyoutwardly of, said first-named condensing surface and thereby being innormal intercepting relation to the radial component of the expandinggas flow to thereby ensure the maximum diffusion of the said gas flowbeing impinged thereon and returned thereby to said first-namedcondensing surface.

8. In a cryopumping system as in claim 6, wherein said second precoolerdevice comprises a. grooved inner surfaceplatelike element disposednormal to the gas flow immediately downstream of said second-namedcondensing surface to thereby intercept, precool, and ensure the returnof the incoming flow in diffused manner to said last-named condensingsurface.

9. In a cryopumping system as in claim 6, wherein said separate coolantsupply and return means comprises a first, inlet coolant supply lineadapted to supply a first coolant at a first, predetermined coolingtemperature; a first manifold in contact with and thereby providingcoolant to said first,

than that of said first-named, cooling temperature and furthercorresponding to the condensation temperature of the gas being condensedthereby; a third manifold in communication between said second, inletcoolant supply line and said first condensing portion; a fourth manifoldfor cooling said second condensing portion; and interconnecting coolanttransfer line means extending between said third and fourth manifoldsfor ensuring the transfer of the said coolant therebetween.

1. A cryopumping system for application in a low-density researchchamber-wind tunnel and/or space propulsion test facility having ahigh-speed nozzle for emitting a high-energy gas flow therefrom, andcomprising; condensing means located in the chamber downstream of thenozzle and incorporating open-ended passageways oriented in a first,predetermined manner relative to the chamber axis, and corresponding toa first position in direct communicating and parallel relation with, andthereby initially receiving and bypassing therethrough the expandingflow of the high-energy gas being emitted from said nozzle, without anysubstantial condensation resulting therefrom; cooling means positionedwithin the chamber at a position therein downstream of the condensingmeans and being further oriented in a second, predetermined mannercorresponding to a second position directly in the path of, and therebyensuring the initial interception and substantial precooling of the gasflow being initially bypassed through the said open-ended passageways ofsaid condensing means; said initially intercepted gas flow being therebyand thereafter returned upstream in a diffused condition, and thereforeat a substantial angle to its original flow, after its initial, directimpingement with said cooling means, for its subsequent and substantialinterception by, and condensation on, a substantial intercepting areaof, the open-ended passageways of said condensing means; and separatecoolant supply and return means adapted to respectively supply coolantat successively lower temperatures to said cooling and condensing means.2. In a cryopumping system as in claim 1, wherein the open-endedpassageways of said condensing means includes separate, first and secondcondensing-passageway portions perpendicularly-arranged relative to eachother and respectively oriented in parallel relation to both radial andaxial-flow components inherent in the expanding gas beinG emitted fromsaid nozzle.
 3. In a cryopumping system as in claim 2, wherein saidfirst condensing-passageway portion comprises a first, plurality ofhorizontally extending and circumferentially-disposed, condensing plateelements arranged in spaced-apart relation to each other, and inparallel relation to the radial component of the said gas flow resultingfrom its radially outward expansion after leaving the chamber nozzle;said condensing plate elements thereby forming said firstcondensing-passageway portion into a plurality of gas flow-bypassingducts aligned in substantially parallel relation to, and thus ensuringthe bypass therethrough of the radial component of said gas flow.
 4. Ina cryopumping system as in claim 2, wherein said secondcondensing-passageway portion comprises a second, plurality ofvertically disposed, condensing plate elements oriented in both spacedapart and parallel relation to each other, and in parallel manner to theaxial component of the said gas flow.
 5. In a cryopumping system as inclaim 4, wherein said cooling means comprises a first, precooler deviceoriented outwardly of, and at a first predetermined angular relation tosaid first, plurality of horizontally disposed, condensing plateelements to thereby ensure the deflection of the radial component ofsaid precooled initial gas flow against a relatively large interceptionarea formed by said condensing means.
 6. In a cryopumping system as inclaim 5, wherein said cooling means further comprises a second precoolerdevice positioned downstream of, and oriented at a second predeterminedangular relation relative to said second, plurality of verticallydisposed, condensing plate elements to thereby ensure the deflection ofthe precooled gas flow against the maximum area of interception of saidlast-named condensing plate elements.
 7. In a cryopumping system as inclaim 5, wherein said first precooler device comprises a grooved andarcuate-shaped, cooling surface circumferentially disposed in spacedrelation to, and radially outwardly of, said first-named condensingsurface and thereby being in normal intercepting relation to the radialcomponent of the expanding gas flow to thereby ensure the maximumdiffusion of the said gas flow being impinged thereon and returnedthereby to said first-named condensing surface.
 8. In a cryopumpingsystem as in claim 6, wherein said second precooler device comprises agrooved inner surface-platelike element disposed normal to the gas flowimmediately downstream of said second-named condensing surface tothereby intercept, precool, and ensure the return of the incoming flowin diffused manner to said last-named condensing surface.
 9. In acryopumping system as in claim 6, wherein said separate coolant supplyand return means comprises a first, inlet coolant supply line adapted tosupply a first coolant at a first, predetermined cooling temperature; afirst manifold in contact with and thereby providing coolant to saidfirst, precooler device and in communication with said first, inletsupply line; a second manifold in contact with and thereby providingcoolant to said second precooler device; and interconnectingcoolant-supply means disposed in open communication between said firstand second manifolds to thereby ensure the transfer of the said coolanttherebetween.
 10. In a cryopumping system as in claim 9, wherein saidseparate coolant supply and return means further comprises a second,inlet coolant supply line adapted to supply a second coolant at asecond, predetermined cooling temperature lower than that of saidfirst-named, cooling temperature and further corresponding to thecondensation temperature of the gas being condensed thereby; a thirdmanifold in communication between said second, inlet coolant supply lineand said first condensing portion; a fourth manifold for cooling saidsecond condensing portion; and interconnecting coolant transfer linemeans extending between said third and fourth manifolds for ensurinG thetransfer of the said coolant therebetween.